Redundant Aircraft Propulsion System Using Co-rotating Propellers Joined By Tip Connectors

ABSTRACT

Multiple propeller blades may be joined by tip connectors to form a closed propeller apparatus. The tip connectors may create continuous structure between adjacent tips of a first propeller and a second propeller. Use of the tip connectors may reduce vortices created near the tips of the propeller blades, which cause drag and slow the rotation of the propeller blades. The tip connectors may also reduce noise caused by rotation of propeller blades. Further, the tip connectors reduce or eliminate deflection of the propeller blades by creating a support structure to counteract forces that would otherwise cause deflection of the propeller blades, thereby improving propeller blade loading. In some embodiments, the tip connectors may be formed of a malleable material and/or include one or more joints that enable at least one of the propellers to modify a pitch of blades of the propeller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to,co-pending, commonly owned U.S. patent application Ser. No. 14/973,610,filed Dec. 17, 2015. U.S. patent application Ser. No. 14/973,610 isfully incorporated herein by reference.

BACKGROUND

Conventional rotor-craft sometimes use multiple propellers (i.e.,rotors) that are sometimes symmetrically located relative to a center ofmass of the aircraft. Each propeller is coupled to a different driveshaft and powered by a different single motor using an electronic speedcontrol (ESC), which controls the rotational speed of the motor, andthus the rotational speed of the propeller. Some rotor-crafts have four,six, eight, or more propellers.

When many propellers are used for propulsion of a rotor-craft, therotor-craft may have some level or redundancy in case of failure of amotor or damage to a propeller. For example, an octocopter may continuecontrolled flight in the event of a failure of one of the motors thatdrive a particular propeller or damage to the particular propellerbecause the other seven propellers can typically maintain flight of theoctocopter even when one propeller is no longer completely functional.However, rotor-craft having fewer propellers may not be able to maintaincontrolled flight in the event of a failure of a motor or damage to apropeller.

Propeller blades, like wings, create vortices during rotation of thepropeller blades. The vortices create drag, which slows the propellerand causes inefficiency. In addition, propeller blades often createundesirable noise during operation at high rotational speeds at leastpartly due to airflow about the tips of blades of the propeller. Whenheavily loaded, propeller blades may deflect, which may reduce someefficiency of the propellers, and may even result in failure of thepropeller if the deflection compromises the structural integrity of thepropeller.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame reference numbers in different figures indicate similar oridentical items.

FIG. 1A is a perspective view of an illustrative redundant aircraftpropulsion system using multiple motors to drive a single shaft coupledto a propeller.

FIG. 1B is an exploded perspective view of the illustrative redundantaircraft propulsion system shown in FIG. 1.

FIG. 2 is a perspective view of an illustrative redundant aircraftpropulsion system using stacked multiple motors to drive a single shaftcoupled to a propeller.

FIG. 3 is a perspective view of an illustrative redundant aircraftpropulsion system using multiple motors that rotate cogwheels thatengage a cogwheel on a shaft coupled to a propeller.

FIG. 4 is a flow diagram of illustrative operation of powering themotors of the redundant aircraft propulsion system in response todetecting a failure of a motor.

FIG. 5A is a perspective view of an illustrative redundant aircraftpropulsion system using multiple motors to drive a single shaft coupledto an illustrative closed propeller apparatus.

FIG. 5B is a side elevation view of the redundant aircraft propulsionsystem shown in FIG. 5A. The motors are positioned on opposite sides ofthe closed propeller apparatus.

FIG. 6 is a side elevation view of a redundant aircraft propulsionsystem having a single motor.

FIG. 7 is a side elevation view of a redundant aircraft propulsionsystem having motors positioned between the propellers.

FIG. 8 is a side elevation view of a redundant aircraft propulsionsystem having a single motor positioned between the propellers.

FIG. 9 is a side elevation view of a redundant aircraft propulsionsystem having a plurality of joints that enable variable pitch operationof at least one of the propellers.

FIG. 10A-10C show illustrative co-propellers having an angle offset inthe plane of rotation of the propellers. FIG. 10A is a perspective viewof the illustrative closed propeller apparatus, FIG. 10B is a top planview of the illustrative closed propeller apparatus, and FIG. 10C is aside elevation view of the illustrative closed propeller apparatus.

FIG. 11A-11C show illustrative co-propellers having different propellersblade profiles and configured in a closed configuration. FIG. 11A is aperspective view of the illustrative closed propeller apparatus, FIG.11B is a top plan view of the illustrative closed propeller apparatus,and FIG. 11C is a side elevation view of the illustrative closedpropeller apparatus.

FIG. 12 is a block diagram of an illustrative unmanned aerial vehicle(UAV) 1200.

DETAILED DESCRIPTION

This disclosure is directed to aircraft propulsion systems. In someembodiments, the aircraft propulsion systems may have redundancy basedon use of multiple motors to drive (rotate) a single shaft coupled to apropeller. The motors may be selected such that a first motor is capableof rotating the drive shaft in an event of a failure of a second motorcoupled to the drive shaft. A one-way clutch bearing, or similar device,may interface between a motor and the drive shaft to enable freerotation of the drive shaft in an event of the motor becominginoperable, such as the motor freezing or locking in a position due tofailure caused by overheating or caused by other conditions or events.Use of the second motor may secure a position of the drive shaft whichmay support the propeller in radial eccentric loading.

In various embodiments, the aircraft propulsion systems may haveredundancy and/or achieve efficiencies using multiple propeller bladesthat are joined by tip connectors to form a closed propeller apparatus.The tip connectors may create continuous structure between adjacent tipsof a first propeller and a second propeller. Use of the tip connectorsmay reduce vortices created near the tips of the propeller blades, whichcause drag and slow the rotation of the propeller blades. The tipconnectors may also reduce noise caused by rotation of propeller blades.Further, the tip connectors reduce or eliminate deflection of thepropeller blades by creating a support structure to counteract forcesthat would otherwise cause deflection of the propeller blades, therebyimproving propeller blade loading. Since both propellers are coupledtogether, the propellers will rotate at the same speed, which mayeliminate a control feature used in some implementations that attempt tomatch rotational speed of different propellers. In some embodiments, thetip connectors may be formed of a malleable material and/or include oneor more joints that enable at least one of the propellers to modify apitch of blades of the propeller.

The closed propeller apparatus may be employed using multiple motors tocreate redundancy in both the power source and also the physicalstructures, such as the propeller blades, the drive shaft, and otherphysical structures. For example, the closed propeller apparatus hasincreased structural rigidity due to the coupling of the propellers bythe tip connectors and possibly by coupling of the propellers by thedrive shaft. This increased structural rigidity may increase adurability of the propeller blades in the event that the propellerblades make contact with another object. The motors may be locatedadjacent to outside surfaces of the closed propeller apparatus or may belocated between the propeller blades.

The apparatuses, systems, and techniques described herein may beimplemented in a number of ways. Example implementations are providedbelow with reference to the figures.

FIG. 1A is a perspective view of an illustrative redundant aircraftpropulsion system 100. The redundant aircraft propulsion system 100 mayinclude using multiple motors 102 to rotate a drive shaft 104 coupled toa propeller 106. Although the propeller 106 is shown as having twoblades, the propeller 106 (and any other propeller described herein) mayhave more propeller blades, such as three blades, four blades, fiveblades, or more. The motors 102 may include a first motor 102(1) and asecond motor 102(2); however, additional motors may also be used in theredundant aircraft propulsion system 100 to achieve similar results. Themotors 102 may be coupled to a frame 108, such as a motor mounting spar,which enables the motors 102 to impart rotation of the drive shaft 104and the propeller 106 relative to the frame 108. The frame 108 may be aframe of an aircraft, such as an unmanned aerial vehicle (UAV), ahelicopter, or other aircraft where the propeller 106 is used to propelthe frame through air vertically, horizontally, or both. However, theframe 108 may be a frame for other devices, such as ground vehicles,maritime vessels, and/or stationary devices, such as fans.

Bearings 110 may be coupled to the drive shaft 104 and other structures,such as the motors 102 and/or the frame 108. In some embodiments, afirst bearing set 110(1) is coupled between the first motor 102(1) andthe drive shaft 104 and a second bearing set 110(2) is coupled betweenthe second motor 102(2) and the drive shaft 104. The bearings 110 mayenable free rotation of the drive shaft 104 in an event of one of themotors 102 (e.g., the first motor 102(1)) becoming inoperable, such asthe first motor 102(1) freezing or locking in a position due to failurecaused by overheating or caused by other conditions or events. In someembodiments, bearings may be coupled between the frame 108 and the driveshaft 104 to secure the drive shaft 104 in an axis 112 of rotation. Invarious embodiments, the motors 102 and/or the bearings 110 may securethe drive shaft 104 in the axis 112 of rotation. For example, use of thesecond motor 102(2) or the second bearing 102(2) in the configurationshown in FIG. 1A may secure a position of the drive shaft 104 andsupport the propeller 106, via the drive shaft 104, during radialeccentric loading.

As shown in FIG. 1A, the first motor 102(1) may be located on a firstside 114 of the propeller 106 while the second motor 102(2) may belocated on the second side 116 of the propeller 106. However, the motors102 may be located in other positions relative to the frame 108 andpropeller. For example, the motors 102 are shown as located betweenopposing structures of the frame 108; however, the motors 102 may belocated outside the opposing structures of the frame 108, for example.As another example, two more motors may be stacked on a same side of thepropeller 106.

During operation, the drive shaft 104 is subject to rotation up to athreshold number of revolutions per minute and up to a threshold torque,due to resistance caused by the propeller 106 moving air or other gasesor fluids. The first motor 102(1) and/or the second motor 102(2) may beselected to operate at a maximum threshold torque that is less than thethreshold torque, such that the combination of the motors 102 inoperation reach or exceed design requirements for long term operation(e.g., continuous rotation of the drive shaft 104 and propeller 106 forup to a predetermined amount of time or indefinitely). In the event thatone of the motors 102 becomes inoperable, the operational motor maycontinue to rotate the drive shaft 104 and the propeller 106, butpossibly for a time less than the predetermined amount of time. Forexample, a single motor may be operated for short periods of time at acapacity that results in excess heat, which if continued for more than athreshold amount of time, may cause the single motor to also fail andbecome inoperable. Thus, operation with a single motor may enableoperations to be performed that do not require peak or near peak output(e.g., do not require lifting or climbing an aircraft in altitude), butmay be used at lower outputs (e.g., to maintain a cruising altitudeand/or successfully land an aircraft).

In some embodiments, three or more motors may be coupled to the driveshaft 104. When one of the motors becomes inoperable, multiple motorsmay still operate to cause the rotation, which may enable use of motorshaving less power, such that a sum of the maximum output of the motorsreaches or exceeds the threshold torque, but possibly exceeds thethreshold torque by less than implementations where fewer motors areused in the redundant aircraft propulsion system 100.

FIG. 1B is an exploded perspective view of the illustrative redundantaircraft propulsion system 100 shown in FIG. 1, which show anillustrative assembly of components of the redundant aircraft propulsionsystem 100. As shown in FIG. 2B, the first motor 102(1) may be locatedproximate to a first portion 104(1) of the drive shaft 104 while thesecond motor 102(2) may be located proximate to a second portion 104(2)of the drive shaft 104.

The bearings 110(1) and 110(2) may include bearing housings 118 and aone-way clutch bearing 120, which is configured to rotate freely in onedirection and prevent rotation in a second direction that is oppositethe first direction. Thus, the one-way clutch bearing 120 may preventrotation (in the second direction), which enables a motor to impartrotational force to the drive shaft 104 via the one-way clutch bearing120. When a motor fails, the bearing freely rotates in the firstdirection as the other motor rotates the drive shaft 104. The bearings110(1)-(2) may be barrel shaped or formed in other shapes to create acompact assembly or form-factor of the redundant aircraft propulsionsystem 100. In some embodiments, the bearings 110 may be integrated withthe motors 102 in a custom motor implementation. Thus the motors 102 mayinclude the one-way clutch bearing 120, which may be coupled to themotor and possibly integrally formed with the motor prior to assembly ofthe redundant aircraft propulsion system 100.

The motors 102 may be brushless direct current (DC) motors and/or othertypes of motors that generated a desired speed of rotation of the driveshaft at a torque experienced during typical operation (e.g., a maximumoperational torque). However, other types of motors may be used, such asDC brush motors, alternating current (AC) motors, gasoline engines,and/or other types of rotation generating devices. In some embodiments,the first motor 102(1) may be a different type of motor than the secondmotor 102(2). As discussed below, gearing systems may also be used,which may be included in the motors or driven by the motors.

The various components of the redundant aircraft propulsion system 100may be coupled using any one of known coupling mechanisms and/orfeatures, including threaded fasteners, adhesives, friction couplings,and/or other types of coupling mechanism/features.

FIG. 2 is a perspective view of an illustrative redundant aircraftpropulsion system 200 using a stacked configuration of multiple motorsto rotate the drive shaft 104 coupled to the propeller 106. The firstmotor 102(1) and the second motor 102(2) may be located on a same sideof the propeller 106, such as on the second side 116 of the propeller106. The motors 102(1)-(2) may be coupled to the frame 108, possiblyusing a coupling support device 202. The coupling support device 202 maysecure a position of the first motor 102(1) relative to the second motor102(2) and/or relative to the frame 108. The redundant aircraftpropulsion system 200 may include the bearings 110(1)-(2), which may belocated between the respective motors and the drive shaft 104 to enablerotation of the drive shaft 104 in the event that one of the motorsbecomes inoperable. The motors 102(1)-(2) and/or the bearings 110(1)-(2)may secure the drive shaft 104 in the axis 112 of rotation.

The redundant aircraft propulsion system 200 may be used inconfigurations where a first side 114 of the propeller is not adjacentto the frame 108, as shown in FIG. 2. For example, when the propeller isused on a fore and/or aft side of a wing or fuselage of an aircraft andwhere the axis 112 is substantially aligned with the horizon of Earthduring forward flight of the aircraft, the frame 108 may only beavailable for coupling on a single side of the propeller 106.

FIG. 3 is a perspective view of an illustrative redundant aircraftpropulsion system 300. The redundant aircraft propulsion system 300 mayinclude the first motors 102(1) and the second motor 102(2) which mayrotate a first cogwheel 302(1) and a second cogwheel 302(2),respectively, directly or using a shaft coupled to a respectivecogwheel. The cogwheels 302(1)-(2) may engage a drive shaft cogwheel 304and cause rotation of the drive shaft cogwheel 304 when at least one ofthe motors 102(1)-(2) is operational. The drive shaft cogwheel 304 iscoupled to the drive shaft 104, which is coupled to the propeller 106.Thus, rotation of one or more of the cogwheels 302(1)-(2) results inrotation of the propeller. The drive shaft 104 may be secured in theaxis 112 of rotation by bearings 306, which may be coupled to the frame108. Although both motors are shown in FIG. 3 as being located proximateto the second side 116 of the propeller 106, the motors could be locatedon either side or on both sides (using another drive shaft cogwheel),and/or in other locations relative to the propeller 106 or the frame108.

The cogwheels 302(1)-(2) may include cogs 308 that engage correspondingdrive shaft cogs 310 on the drive shaft cogwheel 304. The cogs 308 maybe configured to engage the drive shaft teeth 310 during rotation of thecogwheels 302(1)-(2) in a first direction 312 and not engage the driveshaft teeth 310 during rotation of the cogwheels 302(1)-(2) in a seconddirection that is opposite the first direction 312 (from the perspectiveof the drive shaft cogwheel 304). For example, the cogs 308 may bespring loaded and may only cause rotation of the drive shaft cogwheel304, via the drive shaft teeth 310, during rotation in the firstdirection, but may be compressed by the drive shaft cogs 310 and notcause rotation of the drive shaft cogwheel 304 during rotation in thesecond direction (from the perspective of the drive shaft cogwheel 304).Using the spring loaded cogs, or other mechanisms that create a similareffect, the drive shaft 104 may rotate even when one of the motors102(1)-(2) becomes inoperable. Other mechanisms may enable the driveshaft 104 may rotate even when one of the motors 102(1)-(2) becomesinoperable, such as a mechanism that moves the inoperable motor and/orcorresponding cogwheel to prevent the corresponding cogwheel frominhibiting rotation of the drive shaft cogwheel 304, such as a clutchdevice.

In some embodiments, the cogwheels 302(1)-(2) may use the one-way clutchbearings to enable rotation of a first motor in the event that a secondmotor becomes inoperable. The one-way clutch bearings may be employed asdescribed above, such as by interfacing between respective motors andcorresponding shafts that drive the respective cogwheels.

In some embodiments, the at least one of the cogwheel 302(1), thecogwheel 302(2), or both have a different number of cogs than the driveshaft cogwheel 304 to create a geared system. The geared system mayenable gearing up or gearing down, and thus may increase or decrease arotational speed of the drive shaft 104 compared to a rotational speedof one or both of the motors 102(1)-(2).

FIG. 4 is a flow diagram of illustrative process 400 of powering themotors of the redundant aircraft propulsion system in response todetecting a failure of a motor. The process 400 may be performed by anyredundant aircraft propulsion system described herein that uses two ormore motors to rotate a drive shaft coupled to a propeller. The process400 is illustrated as a collection of blocks in a logical flow graph,which represent a sequence of operations that can be implemented inhardware, software, or a combination thereof. It should also beappreciated that the logical flow path depicted in FIG. 4 is not to beconstrued to indicate that the described process operations need beperformed in any particular order unless otherwise expressly andunambiguously stated as such elsewhere herein. Stated alternatively, thelogical flow paths herein represent but a few of many possible orderswhich the steps may be performed. In the context of software, the blocksrepresent computer-executable instructions stored on one or morecomputer-readable storage media (e.g., machine readable storage media)that, when executed by one or more hardware processors, perform therecited operations. Generally, computer-executable instructions includeroutines, programs, objects, components, data structures, and the likethat perform particular functions or implement particular abstract datatypes. Embodiments may be provided as a computer program productincluding a non-transitory computer-readable storage medium havingstored thereon instructions (in compressed or uncompressed form) thatmay be used to program a computer (or other electronic device) toperform processes or methods described herein. The computer-readablestorage medium may include, but is not limited to, hard drives, floppydiskettes, optical disks, CD-ROMs, DVDs, read-only memories (ROMs),random access memories (RAMs), EPROMs, EEPROMs, flash memory, magneticor optical cards, solid-state memory devices, or other types ofmedia/computer-readable medium suitable for storing electronicinstructions. Further, embodiments may also be provided as a computerprogram product including a transitory machine-readable signal (incompressed or uncompressed form). Examples of machine-readable signals,whether modulated using a carrier or not, include, but are not limitedto, signals that a computer system or machine hosting or running acomputer program can be configured to access, including signalsdownloaded. The order in which the operations are described is notintended to be construed as a limitation, and any number of thedescribed blocks can be combined in any order and/or in parallel toimplement the process 400.

At 402, one or more controllers, such as electronic speed controls(ESCs), may power the first motor 102(1) and the second motor 102(2) tocause rotation of the drive shaft 104 and rotation of the propeller 106as described above. The motors may be powered at a first power setting.

At 404, the one or more controllers, a feedback circuit, and/or otherdevice may detect failure of a motor, such as the first motor 102(1).However, the process works similarly upon failure of the second motor102(2). The failure of the motor may cause the motor to be inoperable,and possibly be jammed, frozen, or otherwise incapable of rotation.

At 406, the one or more controllers may increase a power setting of thesecond motor 102(2) in response to the detection at the operation 404.The increase may cause the second motor to operate at more revolutionsper minute for a given input than the first power setting used at theoperation 402. By increasing the power setting for the second motor, thesecond motor may continue to rotate the drive shaft at a rotationalspeed that maintains a desired operation, such as continued flight of anaircraft, for example. In some embodiments where a feedback loop is usedto determine a rotational speed of the drive shaft, the operation 406may be omitted.

At 408, the one or more controllers, such as electronic speed controls(ESCs), may power the second motor 102(2) at the increased power settingto cause rotation of the drive shaft 104 and rotation of the propeller106 as described above, even when the first motor 102(1) is inoperable(e.g., frozen, nonfunctional, etc.). As described above, one-way clutchbearings, or other devices described herein that produce a similareffect, may enable the drive shaft to freely rotate despite theinoperability of the first motor.

At 410, the one or more controllers may update a flight plan when themotors operate a propeller of an aircraft. The update of the flight planmay include causing aircraft to execute a landing and/or limiting orupdating performance expectations/thresholds for the aircraft (e.g.,limiting climbing and/or limiting other power intensive operations). Insome embodiments, the second motor 102(2) may be powerful enough tocontinue flight of an aircraft without any change or without anysignificant change in the flight plan, such as when the second motor102(2) is configured to operate at a maximum threshold torque that isless than a threshold torque, where the drive shaft is subject torotation up to a threshold number of revolutions per minute and up tothe threshold torque.

FIG. 5A is a perspective view of an illustrative redundant aircraftpropulsion system 500. The redundant aircraft propulsion system 500includes a closed propeller apparatus 502 that includes a firstpropeller 504 (sometimes referred to herein as a top propeller) coupledto a second propeller 506 (sometimes referred to herein as a bottompropeller) by a first tip connector 508(1) and a second tip connector508(2). The first tip connector 508(1) may couple a first tip 510 of thefirst propeller 504 to a second tip 512 of the second propeller 506 tocreate a continuous structure joining the first propeller 504 to thesecond propeller 506. Likewise, the second tip connector 508(2) maycouple adjacent tips of the propellers 504, 506. A cross-section of thetip connectors may resemble a tear drop or other aerodynamic profilethat has minimal drag while having structural rigidity.

Although the first propeller 504 and the second propeller 5069 are shownas having two blades, the propellers (and any other propeller describedherein) may have more propeller blades, such as three blades, fourblades, five blades, or more, which may be coupled together in a similarmanner using corresponding tip connectors. A distance between the firstpropeller 504 and the second propeller 506 may be selected to createoptimal thrust from the respective propellers.

Use of the tip connectors 508(1)-(2) may reduce vortices created nearthe tips 510, 512 of the propellers 504, 506, which cause drag and slowthe rotation of the propeller blades. The tip connectors 508(1)-(2) mayalso reduce noise caused by rotation of propellers. Further, the tipconnectors 508(1)-(2) reduce or eliminate deflection of the propellersby creating a support structure to counteract forces that wouldotherwise cause deflection of the propellers, thereby improvingpropeller blade loading. Since both propellers are coupled together, thepropellers will rotate at the same speed, which may eliminate a controlfeature used in some implementations that attempt to match rotationalspeed of different propellers. In some embodiments, the tip connectors508(1)-(2) may be formed of a malleable material and/or include one ormore joints that enable at least one of the propellers to modify a pitchof blades of the propeller.

As shown in FIG. 5A, the first propeller 504 and the second propeller506 may rotate about the same axis 112 and may rotate in rotationalplanes that are parallel to one other. The closed propeller apparatus502 may include the drive shaft 104, which may be coupled to the closedpropeller apparatus 502, and possibly integrally formed with the closedpropeller apparatus 502. The drive shaft 104 may create additionalsupporting structure for the closed propeller apparatus 502, which is inaddition to the tip connectors 508(1)-(2), which also provide supportingstructure for the closed propeller apparatus 502.

The drive shaft 104 may be coupled to the motors 102(1)-(2), possiblyvia the one-directional clutch bearings 110(1)-(2), as discussed abovewith reference to FIG. 1A. In some embodiments, the redundant aircraftpropulsion system 500 may include a single motor to rotate the driveshaft 104 and, therefore, may not have the motor redundancy as describedabove with reference FIG. 1A.

FIG. 5B is a side elevation view of the redundant aircraft propulsionsystem 500 shown in FIG. 5A. The first propeller 504 may include a firstpitch 514 while the second propeller 506 may include a second pitch 516.The pitch may be an angle of propeller blades rotated about an axis thatis perpendicular to a line tangent to the drive shaft. The greater thepitch, the more air the propeller blades move during rotation.

In some embodiments, the first pitch 514 and the second pitch 516 may befixed pitches and thus not configured for movement of propeller bladeswith respect to a spinner (hub) or axis of rotation. The first pitch 514and the second pitch 516 may or may not be equivalent. For example, thefirst pitch 514 may have a lesser angle (and thus move less air) thanthe second pitch 516. However, the first pitch 514 may be greater thanthe second pitch 516 in some implementations. Use of propellers havingdifferent blade designs or profiles is discussed in more detail withreference to FIGS. 11A-C.

In various embodiments, the first propeller 504, the second propeller506, or both may be configured for variable pitch, such as by use ofactuators that cause a pitch (or angle) of propeller blades to changerelative to the spinner (hub) by mechanically rotating the blades aboutan axis that is perpendicular to a line tangent to the drive shaft. Insuch embodiments, the tip connectors 508(1)-(2) may include malleableportions 518 which may enable a change in the pitch of the blades of thefirst propeller 504, the second propeller 506, or both. The malleablestructure 518 may be formed of rubber, plastic, and/or other malleablesubstances that enable some deformation while still providingcompression forces against the respective propellers and while generallymaintaining a design profile, such as curved radiuses 520. The curvedradiuses 520 may be selected to minimize drag and/or minimize noisecaused during rotation of the closed propeller apparatus 502. Thus, themalleable structure 518 enables movement of the pitch of the bladeswhile maintaining the continuous structure joining the first propeller504 and the second propeller 506. In various embodiments, the malleablestructure 518 may enable a dynamic change to an offset between the firstblade 504 and the second blade 506, which may be performed based on arotational speed of the closed propeller apparatus, for example.Actuators may be used to move the propellers together or apart to varythe offset.

FIG. 6 is a side elevation view of a redundant aircraft propulsionsystem 600 having a single motor 602. As shown, the redundant aircraftpropulsion system 600 may include the frame 108 on a first side of theclosed propeller apparatus 502 that is used in part to secure the motor602. The drive shaft 104 may or may not extend between the firstpropeller 504 and the second propeller 506. For example, when the driveshaft 104 does not extend between the propellers, the tip connectors508(1)-(2) may transfer rotation imparted by the motor 602 to the firstpropeller 504 when the motor 602 causes the second propeller 506 torotate.

FIG. 7 is a side elevation view of a redundant aircraft propulsionsystem 700. The redundant aircraft propulsion system 700 may include thefirst motor 102(1) and the second motor 102(2) located between the firstpropeller 504 and the second propeller 506. Location of the motorsbetween the propellers may enable a smaller form factor (or envelope) tocontain the redundant aircraft propulsion system 700. In someembodiments, the redundant aircraft propulsion system 700 may includethe one-way clutch bearings 110(1)-(2), which may be located between themotors and the propellers.

The redundant aircraft propulsion system 700 may include bearings 702 tosecure a drive shaft 704 along the axis 112 of rotation. The drive shaft704 may include a fixed body, possibly within a rotatable exterior bodyof the drive shaft 704, which is stationary and used to fix the motorsto the frame 108. The fixed body may be used to power the motors whilethe rotatable exterior body may be coupled to the propellers and/or theone-way clutch bearings 110(1)-(2) to cause rotation thereof. However,other configurations may be used for the drive shaft 704, such as aconfiguration that has the fixed body outside of a rotating inner body.

FIG. 8 is a side elevation view of a redundant aircraft propulsionsystem 800 having a single motor 802 positioned between the co-rotatingpropellers. In some embodiments, the single motor may be located outsideof the closed propeller apparatus 502 rather than between the propellers504, 506. In such instances, the frame 108 may not include a support oneach side of the closed propeller apparatus 502.

FIG. 9 is a side elevation view of a redundant aircraft propulsionsystem 900 having a plurality of joints that enable variable pitchoperation of at least one of the propellers. In various embodiments, thefirst propeller 504, the second propeller 506, or both may be configuredfor variable pitch, such as by use of actuators 906(1) and/or 906(2)that cause a pitch (or angle) of propeller blades to change bymechanically rotating the blades about an axis that is perpendicular toa line tangent to the drive shaft. In such embodiments, a first joint902 may be located on the tip connector 508(1) or between the tipconnector 508(1) and the first tip 510. A second joint 904 may belocated on the tip connector 508(2) or between the tip connector 508(2)and the second tip 512. Additional joints may be used to enable a smoothand continuous shape of the tip connectors 508(1)-(2), even after achange in pitch of one or more propeller blades, via the actuators906(1) and/or 906(2). The additional joints may also be used to create alinkage as discussed below. In some embodiments, the joints may form achain-like linkage that comprises many different movable parts.

The joints 902, 904 may enable a change in the pitch of the blades ofthe first propeller 504, the second propeller 506, or both. The joints902, 904 may permit a change in the pitch of blades while generallymaintaining a design profile of the closed propeller apparatus 502, suchas the curved radiuses 520. The curved radiuses 520 may be selected tominimize drag and/or minimize noise caused during rotation of the closedpropeller apparatus 502. Thus, the joints 902, 904 enable movement ofthe pitch of the blades while maintaining the continuous structurejoining the first propeller 504 and the second propeller 506. In someembodiments, the joints 902, 904 may create a linkage system thatenables a single actuator or actuators 906(1)_of the first propeller 504to modify the pitch of blades of the second propeller 506 bymechanically transferring the changes of the pitch from the firstpropeller 504 to the second propeller.

In some embodiments, the joints 902, 904 may enable rotation of the tipconnector 508(1), the tip connector 504(2), or both in a way that causesan air break, which may act to slow the rotational speed of the closedpropeller apparatus 502. In various embodiments, modifications to theangle or orientation of the tip connectors relative to the propellers504,506 may also result in different amounts of noise being generatedduring rotation of the closed propeller apparatus 502. In variousembodiments, the joints 902, 904 may enable a dynamic change to anoffset between the first blade 504 and the second blade 506, which maybe performed based on a rotational speed of the closed propellerapparatus, for example. Actuators may be used to move the propellerstogether or apart to vary the offset.

FIG. 10A-10C show an illustrative closed propeller apparatus 1000. FIG.10A is a perspective view of the closed propeller apparatus. As shown inFIG. 10A, the closed propeller apparatus 1000 may include the firstpropeller 504 and the second propeller 506 that are connected at tipsvia tip connectors 1002(1) and 1002(2), which create a continuousstructure, similar to the tip connectors 508(1)-(2).

The first propeller 504 may include a first longitudinal axis 1004 whilethe second propeller 506 may include a second longitudinal axis 1006. Asshown in FIG. 10B, which is a top plan view of the closed propellerapparatus 1000, the first longitudinal axis 1004 may include an angleoffset □ 1008 such that the second propeller 506 trails the firstpropeller 504 during rotation of the closed propeller apparatus 1000.However, in some embodiments, the angle offset □ 1008 may be configuredsuch that the first propeller 504 trails the second propeller 506 duringrotation of the closed propeller apparatus 1000. FIG. 10C is a sideelevation view of the closed propeller apparatus 1000. Stated anotherway, the angle offset □ 1008 is an angular difference of the firstpropeller 504 and the second propeller 506 in a plane of rotation of thepropellers. When the angle offset □ 1008 is greater than zero, the firstlongitudinal axis 1004 is not parallel to the second longitudinal axis1006.

The angle offset □ 1008 may cause the second propeller 506 to movethorough laminar or “cleaner” air than would otherwise happen when noangular offset is used (e.g., □=0). The angle offset □ 1008 may be anyangle up to 90 degrees, however, angles over 45 degrees may beimpractical due to constraints in creating long versions of the tipconnectors 1002(1)-(2) to span across such a distance and the extraweight and complexity involved with such a design. The angle offset □1008 may be selected to create optimal thrust from the respectivepropellers. The use of the angle offset may also be incorporated withany of the other features discussed herein, including use of variablepitch or different propeller blade profiles (or designs), which isdiscussed immediately below.

FIG. 11A-11C show illustrative closed propeller apparatus 1100. Theclosed propeller apparatus 1100 includes different propellers bladeprofiles. FIG. 11A is a perspective view of the closed propellerapparatus 1100. As shown in FIG. 11A, the closed propeller apparatus1100 may include the first propeller 504 and the second propeller 506that are connected at tips via tip connectors 1102(1) and 1102(2), whichcreate a continuous structure, similar to the tip connectors 508(1)-(2).

The first propeller 504 may include a first blade profile (or design)1104 while the second propeller 506 may include a second blade profile(or design) 1106. The blade designs may cause the propeller to move airin a different way, which when properly tuned, may increase thrustgenerated by the closed propeller apparatus 1100.

FIG. 11B is a top plan view of the closed propeller apparatus 1100,while FIG. 11C is a side elevation view of the closed propellerapparatus 1100. The blade designs for the first propeller 504 and thesecond propeller 506 may be selected to create optimal thrust from therespective propellers. In some embodiments, the blade profile mayinclude a pitch of the blade, a length of the blade, a length of apitched portion of the blade, a radius of the blade's leading edgeand/or trailing edge, and/or other design factors for propeller blades.

FIG. 12 is a block diagram of an illustrative unmanned aerial vehicle(UAV) 1200. The UAV 1200 may be used to implement the various systems,devices, and techniques discussed above. In the illustratedimplementation, the UAV 1200 includes one or more processors 1202,coupled to a non-transitory computer readable media 1220 via aninput/output (I/O) interface 1210. The UAV 1200 may also include apropeller motor controller 1204, power supply module 1206 and/or anavigation system 1208. The UAV 1200 further includes an inventoryengagement mechanism controller 1212, a network interface 1216, and oneor more input/output devices 1218.

In various implementations, the UAV 1200 may be implemented using auniprocessor system including one processor 1202, or a multiprocessorsystem including several processors 1202 (e.g., two, four, eight, oranother suitable number). The processor(s) 1202 may be any suitableprocessor capable of executing instructions. For example, in variousimplementations, the processor(s) 1202 may be general-purpose orembedded processors implementing any of a variety of instruction setarchitectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, orany other suitable ISA. In multiprocessor systems, each processor(s)1202 may commonly, but not necessarily, implement the same ISA.

The non-transitory computer readable media 1220 may be configured tostore executable instructions/modules, data, flight paths, and/or dataitems accessible by the processor(s) 1202. In various implementations,the non-transitory computer readable media 1220 may be implemented usingany suitable memory technology, such as static random access memory(SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory,or any other type of memory. In the illustrated implementation, programinstructions and data implementing desired functions, such as thosedescribed above, are shown stored within the non-transitory computerreadable memory as program instructions 1222, data storage 1224 andflight path data 1226, respectively. In other implementations, programinstructions, data and/or flight paths may be received, sent or storedupon different types of computer-accessible media, such asnon-transitory media, or on similar media separate from thenon-transitory computer readable media 1220 or the UAV 1200. Generallyspeaking, a non-transitory, computer readable memory may include storagemedia or memory media such as flash memory (e.g., solid state memory),magnetic or optical media (e.g., disk) coupled to the UAV 1200 via theI/O interface 1210. Program instructions and data stored via anon-transitory computer readable medium may be transmitted bytransmission media or signals such as electrical, electromagnetic, ordigital signals, which may be conveyed via a communication medium suchas a network and/or a wireless link, such as may be implemented via thenetwork interface 1216.

In one implementation, the I/O interface 1210 may be configured tocoordinate I/O traffic between the processor(s) 1202, the non-transitorycomputer readable media 1220, and any peripheral devices, the networkinterface or other peripheral interfaces, such as input/output devices1218. In some implementations, the I/O interface 1210 may perform anynecessary protocol, timing or other data transformations to convert datasignals from one component (e.g., non-transitory computer readable media1220) into a format suitable for use by another component (e.g.,processor(s) 1202). In some implementations, the I/O interface 1210 mayinclude support for devices attached through various types of peripheralbuses, such as a variant of the Peripheral Component Interconnect (PCI)bus standard or the Universal Serial Bus (USB) standard, for example. Insome implementations, the function of the I/O interface 1210 may besplit into two or more separate components, such as a north bridge and asouth bridge, for example. Also, in some implementations, some or all ofthe functionality of the I/O interface 1210, such as an interface to thenon-transitory computer readable media 1220, may be incorporateddirectly into the processor(s) 1202.

The propeller motor(s) controller 1204 communicates with the navigationsystem 1208 and adjusts the power of each propeller motor to guide theUAV along a determined flight path. The power supply module 1206 maycontrol the charging and any switching functions associated with one ormore power modules (e.g., batteries) of the UAV.

The navigation system 1208 may include a GPS or other similar systemthat can be used to navigate the UAV to and/or from a location. Theinventory engagement mechanism controller 1212 communicates with theactuator(s) or motor(s) (e.g., a servo motor) used to engage and/ordisengage inventory. For example, when the UAV is positioned over alevel surface at a delivery location, the inventory engagement mechanismcontroller 1212 may provide an instruction to a motor that controls theinventory engagement mechanism to release the inventory.

The network interface 1216 may be configured to allow data to beexchanged between the UAV 1200, other devices attached to a network,such as other computer systems, and/or with UAV control systems of otherUAVs. For example, the network interface 1216 may enable wirelesscommunication between numerous UAVs. In various implementations, thenetwork interface 1216 may support communication via wireless generaldata networks, such as a Wi-Fi network. For example, the networkinterface 1216 may support communication via telecommunications networkssuch as cellular communication networks, satellite networks, and thelike.

Input/output devices 1218 may, in some implementations, include imagecapture devices, infrared sensors, time of flight sensors,accelerometers, lights, speakers, and other input/output devicescommonly used in aviation. Multiple input/output devices 1218 may bepresent and controlled by the UAV 1200. One or more of these sensors maybe utilized to assist in landings as well as avoiding obstacles duringflight.

In various implementations, the parameter values and other dataillustrated herein as being included in one or more data stores may becombined with other information not described or may be partitioneddifferently into more, fewer, or different data structures. In someimplementations, data stores may be physically located in one memory ormay be distributed among two or more memories.

Those skilled in the art will appreciate that the UAV 1200 is merelyillustrative and is not intended to limit the scope of the presentdisclosure. In particular, the computing system and devices may includeany combination of hardware or software that can perform the indicatedfunctions, including computers, network devices, internet appliances,PDAs, wireless phones, pagers, etc. The UAV 1200 may also be connectedto other devices that are not illustrated, or instead may operate as astand-alone system. In addition, the functionality provided by theillustrated components may in some implementations be combined in fewercomponents or distributed in additional components. Similarly, in someimplementations, the functionality of some of the illustrated componentsmay not be provided and/or other additional functionality may beavailable.

Those skilled in the art will also appreciate that, while various itemsare illustrated as being stored in memory or storage while being used,these items or portions of them may be transferred between memory andother storage devices for purposes of memory management and dataintegrity. Alternatively, in other implementations, some or all of thesoftware components may execute in memory on another device andcommunicate with the illustrated UAV 1200. Some or all of the systemcomponents or data structures may also be stored (e.g., as instructionsor structured data) on a non-transitory, computer-accessible medium or aportable article to be read by an appropriate drive, various examples ofwhich are described above. In some implementations, instructions storedon a computer-accessible medium separate from the UAV 1200 may betransmitted to the UAV 1200 via transmission media or signals such aselectrical, electromagnetic, or digital signals, conveyed via acommunication medium such as a wireless link. Various implementationsmay further include receiving, sending or storing instructions and/ordata implemented in accordance with the foregoing description upon acomputer-accessible medium. Accordingly, the techniques described hereinmay be practiced with other UAV control system configurations.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as illustrative forms ofimplementing the claims.

What is claimed is:
 1. An apparatus comprising: a frame; a drive shaft;a propeller coupled to the drive shaft, a first portion of the driveshaft located proximate to a first side of the propeller; a first motorcoupled to the first portion of drive shaft; a second motor coupled tothe first portion of the drive shaft, wherein power input from at leastone of the first motor or the second motor causes rotation of the driveshaft and the propeller, and wherein at least one of the first motor orthe second motor is coupled to the frame; a first clutch bearing coupledto the first motor, wherein the first clutch bearing enables therotation of the drive shaft upon a first failure of the first motorwhile the second motor is in operation; and a second clutch bearingcoupled to the second motor, wherein the second clutch bearing enablesthe rotation of the drive shaft upon a second failure of the secondmotor while the first motor is in operation.
 2. The apparatus as recitedin claim 1, further comprising a first cogwheel coupled to at least oneof the first motor or the second motor and a second cogwheel coupled tothe drive shaft, and wherein the first cogwheel engages the secondcogwheel to enable at least one of the first motor or the second motorto drive the rotation of the drive shaft.
 3. The apparatus as recited inclaim 1, wherein the first motor is configured to operate at a firstpower setting, the first power setting including the first motoroperating at a first number of revolutions per minute (RPM), and whereinthe first motor is further configured to operate at a second powersetting upon the second failure of the second motor, the second powersetting including the first motor operating at a second number of RPMthat is greater than the first number of RPM.
 4. The apparatus asrecited in claim 1, further comprising a coupling support device thatsecures a first position of the first motor relative to at least one ofa second position of the second motor or a third position of the driveshaft.
 5. An apparatus comprising: a drive shaft; a propeller coupled tothe drive shaft; a first motor coupled to at least one of the driveshaft or a second motor; and the second motor coupled to at least one ofthe drive shaft or the first motor, wherein power output from at leastone of the first motor or the second motor causes rotation of the driveshaft and the propeller.
 6. The apparatus as recited in claim 5, whereinthe propeller includes a first side, the drive shaft includes a firstportion of the drive shaft extending from the first side, and whereinthe first motor and the second motor are coupled to the first portion ofthe drive shaft.
 7. The apparatus as recited in claim 6, furthercomprising a coupling support device that secures a first position ofthe first motor relative to at least one of a second position of thesecond motor or a third position of the drive shaft.
 8. The apparatus asrecited in claim 5, further comprising a frame that is coupled to atleast one of the first motor or the second motor.
 9. The apparatus asrecited in claim 5, further comprising a first cogwheel coupled to atleast one of the first motor or the second motor and a second cogwheelcoupled to the drive shaft, and wherein the first cogwheel engages thesecond cogwheel to enable at least one of the first motor or the secondmotor to drive the rotation of the drive shaft.
 10. The apparatus asrecited in claim 9, wherein the second cogwheel is coupled to a framevia a clutch bearing, the first cogwheel including a first number ofcogs and the second cogwheel including a second number of cogs that isdifferent than the first number of cogs.
 11. The apparatus as recited inclaim 5, wherein the first motor is coupled to a first clutch bearing,the second motor is coupled to a second clutch bearing, the first clutchbearing enables the rotation of the drive shaft upon a first failure ofthe first motor and the second clutching bearing enables the rotation ofdrive shaft upon a second failure of the second motor.
 12. The apparatusas recited in claim 11, wherein the first motor is configured to operateat a first power setting, the first power setting including the firstmotor operating at a first number of revolutions per minute (RPM), andwherein the first motor is further configured to operate at a secondpower setting upon the second failure of the second motor, the secondpower setting including the first motor operating at a second number ofRPM that is greater than the first number of RPM.
 13. The apparatus asrecited in claim 11, wherein at least one of the first failure of thefirst motor or the second failure of the second motor includes at leastone of overheating, freezing, locking, jamming, or a failure to rotate.14. The apparatus as recited in claim 5, wherein the propeller is afirst propeller, and further comprising: a second propeller coupled tothe drive shaft; a first connector to couple a first portion of thefirst propeller to a first portion of the second propeller; and a secondconnector to couple a second portion of the first propeller to a secondportion of the second propeller.
 15. The apparatus as recited in claim14, wherein the first connector and the second connector create acontinuous structure joining the first propeller and the secondpropeller, and wherein at least one of the first connector or the secondconnector includes at least one of a malleable portion or a joint. 16.An unmanned aerial vehicle (UAV) comprising: a frame; a power sourcecoupled to the frame; and a propulsion unit, wherein the propulsion unitincludes: a drive shaft; a propeller coupled to the drive shaft; and afirst motor coupled to at least one of the drive shaft or a secondmotor, wherein the second motor is coupled to at least one of the driveshaft or the first motor, and wherein power output from at least one ofthe first motor or the second motor causes rotation of the drive shaftand the propeller.
 17. The UAV as recited in claim 16, wherein thepropulsion unit further includes: a first cogwheel coupled to at leastone of the first motor or the second motor; and a second cogwheelcoupled to the drive shaft, wherein the first cogwheel engages thesecond cogwheel to enable at least one of the first motor or the secondmotor to drive the rotation of the drive shaft.
 18. The UAV as recitedin claim 16, wherein the first motor is coupled to a first clutchbearing, the second motor is coupled to a second clutch bearing, and thefirst clutch bearing enables the rotation of the drive shaft upon afirst failure of the first motor and the second clutching bearingenables the rotation of drive shaft upon a second failure of the secondmotor.
 19. The UAV as recited in claim 16, wherein the propellerincludes a first side, the drive shaft includes a first portion of thedrive shaft extending from the first side, and the first motor and thesecond motor are coupled to the first portion of the drive shaft. 20.The UAV as recited in claim 16, wherein the propeller is a firstpropeller, and the propulsion unit further includes: a second propellercoupled to the drive shaft; a first connector that couples a firstportion of the first propeller to a first portion of the secondpropeller; and a second connector that couples a second portion of thefirst propeller to a second portion of the second propeller.